Applications of the rotating photobioreactor

ABSTRACT

A method to recover and harvest nutrients from a liquid stream by incorporating them into microorganisms grown in a rotating photobioreactor. The method further includes optionally integrating the rotating photobioreactor with a composting or biogenic drying process.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of provisional Application No.61/743,380 by the same applicant for the same invention, filed Sep. 4,2012, and is a continuation-in-part of application Ser. No. 13/373,860,filed on Dec. 1, 2011. Application Ser. No. 13/373,860 claims thebenefit of provisional Application No. 61/460,219, filed Dec. 29, 2010.All of the above are incorporated herein expressly by reference in theirentirety.

STATEMENT REGARDING GOVERNMENT RESEARCH

The U.S. Department of Agriculture funded proof of concept researchunder U.S. Department of Agriculture 2010 SBIR project number2010-33610-20920.

BACKGROUND OF THE INVENTION

1. Field of Invention

This invention is a bioreactor that can support a large fixed microbialor autotrophic biofilm that consumes soluble organic or inorganicsubstrates while producing a nutrient rich biomass and gases such ashydrogen, oxygen, biofuels, and ammonia, that are harvested for abeneficial purpose. This invention can be applied to a variety ofprocesses for recovering valuable gases, nutrients, and productsproduced from different substrates by autotrophic organisms in a singlereactor without the use of chemicals and with minimal energy inputs.Applications include nutrient removal and harvesting from a variety ofwater bodies, volatile or semi-volatile gas stripping, concentration ofstripped gases, and compost biogenic drying.

2. Background

Nutrients discharged from agricultural operations, waste management, andbioenergy processing facilities are significant environmental problemsadversely affecting over 30% of our nations waters. The National Academyof Engineering of the National Academies recently published the “GrandChallenges for Engineering,” posted athttp://www.engineeringchallenges.org/cms/challenges.aspx. One of the 14challenges was “Manage the Nitrogen Cycle”. The “nitrogen issue” is theresult of twice as much nitrogen being introduced into the world throughanthropogenic sources as introduced from natural sources. The ability toproduce reactive nitrogen through the Haber-Bosch process has enabledman to feed the world. However, that engineering miracle has totallydistorted the nitrogen cycle leading to significant environmental andpublic health problems. Seventy five percent of the additionalanthropogenic reactive nitrogen input is converted to N₂ gas throughdenitrification, a process that converts a portion (2% to 6%) of thenitrogen to the powerful greenhouse gas N₂O, which has an atmosphericlifetime of over 100 years. Aside from being a powerful GHG at 310 timesCO₂, N₂O is now the primary cause of stratospheric ozone depletion. Theremaining 25% of the added reactive nitrogen is accumulated in thesoils, groundwater, rivers, estuaries, and oceans modifying thoseterrestrial and aquatic environments. The adverse impacts of nitrogeninclude the production of fine particulate matter that is responsiblefor atmospheric haze and increased human mortality, increased nitratelevels in groundwater, acidification of surface water, harmful toxinproducing algae blooms, hypoxia in coastal waters, forestry decline, andloss of terrestrial biodiversity.

Solutions to the “nitrogen problem” have primarily been through the useof engineered denitrification systems that increase the NOx, N₂O, andfine particulate matter emissions to the atmosphere. Some processesattempt to recover and reuse ammonia and thereby reduce the industrialproduction of ammonia through the Haber-Bosch process. Ion exchange,membrane separation, and stripping technologies have all been used. Therecovery processes invariably sequester the ammonia as dilute acidicsolutions of ammonium sulfate or ammonium nitrate. Those processes havebeen shown to be uneconomical technologies.

Soluble phosphorus and nitrogen are the primary concern. Technology isrequired to economically remove soluble nitrogen, phosphorus, andpotassium nutrients discharged from waste treatment, agriculturalfields, or bioenergy facilities. Such facilities include manuremanagement, food processing, wastewater treatment, and renewable energyproduction such as anaerobic digestion where a majority of theparticulate organic nutrients are converted to soluble ammonia andphosphate.

A large variety of expensive technologies have been developed to removeboth soluble nitrogen and phosphate from wastewater streams. Phosphateremoval by chemical precipitation, biological assimilation, orcrystallization (MAP, struvite) precipitation is expensive. Ammonianitrogen removal by stripping, biological nitrification/denitrification,ammonia oxidation (Anammox) or precipitation as ammonium sulfate,nitrate, or phosphate is also expensive. Wetlands or constructed marshesare the least expensive but occupy large tracts of land where nutrientaccumulation may not be sustainable.

Conversion of soluble nutrients to particulate matter, such as micro andmacro algae is an attractive method for removing soluble nutrients.However, the limited productivity, ammonia toxicity, and cost ofharvesting have prevented widespread adoption. Algae or cyanobacteriagrowth is limited by the turbidity that such growth imparts to theliquid. Light penetration is reduced in direct proportion to the algaebiomass concentration. Pond surface area also limits CO₂ transfer to thegrowing algae thereby limiting productivity. Variable depth and energyconsuming gas injection photobioreactors have been proposed to overcomesuch limitations.

Ammonia toxicity is also a significant problem requiring dilutions of upto 20 to 1 for anaerobic digestate. Ammonia concentrations exceeding 100ppm are inhibitory to autotrophic growth. Nitrogen loss to theatmosphere is also a significant problem in high pH systems. The loss ofnitrogen to the atmosphere led the National Academy of Science toconclude that the growth of algae for biofuel production wasunsustainable. “The estimated requirement for nitrogen and phosphorusneeded to produce algal biofuels necessary to meet 5% of UStransportation fuel ranges from 6 million to 15 million metric tons ofnitrogen and from 1 million to 2 million metric tons of phosphorus ifthe nutrients are not recycled or included and used in co-products.Those estimated requirements represent 44 to 107 percent of the totalnitrogen use and 20 to 51 percent of total phosphorus use in the UnitedStates.”

Finally, harvesting a highly concentrated biomass containing therecovered nutrients is expensive. The algae biomass separation andconcentration is the most expensive unit process, representing 20 to 30%of the total cost of algae production and recovery systems. The limitedproductivity results in slow nutrient recovery in larger than desiredreactors. Additional equipment for biomass nutrient separation andconcentration increases the cost considerably.

The autotrophic rotating photobioreactor (RPB) is similar to theheterotrophic rotating biological contactor (RBC), a waste treatmentdevice used to support large heterotrophic bacterial populations for theenhanced removal of soluble organic waste constituents flowing throughthe RBC. In fact, a rotating bioreactor contactor can be converted intoa rotating photobioreactor by adding to it a light source directed atthe microorgisms, using autotrophic micoorganisms, and providing acarbon source, such as carbon dioxide or bicarbonate. A variety ofconfigurations and devices exist for heterotrophic waste treatment. Thefollowing U.S. patents are representative of the development of the art:U.S. Pat. No. 1,811,181 (an original disclosure of an open RBC, issuedin 1931); U.S. Pat. No. 1,947,777 (an enclosed heat exchanger,adsorption unit, issued in 1934); U.S. Pat. No. 3,630,366 (the typicalopen conventional RBC, issued in 1971); U.S. Pat. No. 3,704,783 (anaerated fixed film RBC, issued in 1972); U.S. Pat. No. 3,904,525 (apre-aerated spray RBC issued in 1975); U.S. Pat. No. 4,115,268 (an openor closed RBC with an alternative rotor design, issued in 1978); U.S.Pat. No. 4,137,172 (an attached growth RBC with corrugated disks,operating at 40% submergence, issued in 1979); U.S. Pat. No. 4,289,620(a RBC in combination with an adsorbent, issued in 1981); U.S. Pat. No.4,330,408 (a partially submerged RBC incorporating suffusing a portionof disc with air, issued in 1982); U.S. Pat. No. 4,345,997 (an RBC withunique disc ribs, issued in 1982); U.S. Pat. No. 4,385,987 (a RBC withalternative structural design of the discs, issued in 1983); U.S. Pat.No. 4,431,537 issued in 1984; U.S. Pat. No. 4,444,658 issued in 1984);U.S. Pat. No. 4,537,678 issued in 1985); U.S. Pat. No. 4,549,962 issuedin 1985); U.S. Pat. No. 5,401,398 issued in 1995); U.S. Pat. No.

5,458,817, issued in 1995); U.S. Pat. No. 5,498,376 issued in 1996; U.S.Pat. No. 5,637,263 issued in 1997); U.S. Pat. No. 5,714,097 issued in1998); U.S. Pat. No. 5,851,636 (ceramic plates) issued in 1998); U.S.Pat. No. 6,071,593 (grooved ceramic packing) issued in 2000); U.S. Pat.No. 6,241,222 issued in 2001); U.S. Pat. No. 6,783,669 issued in 2004);U.S. Pat. No. 7,156,986 issued in 2007); U.S. Pat. No. 8,460,548 issuedin 2013); U.S. Pat. No. 4,563,282 (a RBC incorporating microscreens inconjunction with rotating biological contactors that are placed in aprimary settling tank, the aeration tank and a final clarification tank,issued in 1986); U.S. Pat. No. 4,568,457 (an anaerobic RBC incorporatingacid and methane phase segments, issued in 1986); U.S. Pat. No.4,604,206 (a staged anaerobic digestion RBC, issued in 1986); U.S. Pat.No. 4,668,387 (an aerated, completely submerged air-driven RBC, issuedin 1987); U.S. Pat. No. 4,692,250 (a recirculating staged waste watertreatment RBC, issued in 1987); U.S. Pat. No. 4,721,570 (a RBC with asolids contact zone, issued in 1988); Nos. 4,729,828 and 4,737,278 (amodular rotating biological contactor apparatus, issued in 1988); U.S.Pat. No. 5,326,459 (a two-stage RBC with different diameter discs,issued in 1994); U.S. Pat. No. 5,395,528 (a complex sewage treatmentapparatus incorporating a RBC, issued in 1995); U.S. Pat. No. 5,407,578(a partitioned RBC capable of addressing toxic inputs, issued in 1995);U.S. Pat. No. 5,853,591 (a hydraulically driven RBC, issued in 1998);U.S. Pat. No. 6,403,366 (a rotating biofilter scrubber for removing airpollutants, issued in 2002); U.S. Pat. No. 7,083,720 (a modularexpandable RBC, issued in 2006); U.S. Pat. No. 8,191,868 (a RotatingInverse Biological Contactor (RIBC), issued in 2012); and U.S. Pat. No.8,398,828 (an RBC incorporating photocatalytic degradation with UVlight, issued in 2013). Relevant U.S. patent applications include: No.20050133444 (self-cleansing media, filed in 2005); a patent applicationfor a double-sided, self-cleaning media, filed in 2007; No. 20080053880(configurable RBC application, filed in 2008); No.

20080210610 (RBC that could be inoculated with various bacteria, filedin 2008).

The patent history displays a wide variety of configurations andarrangements for the aerobic or anaerobic treatment of wastewaterthrough the retained growth of a bacterial biofilm on the RBC rotatingsurface in open or enclosed reactors. A large heterotrophic, as opposedto autotrophic biomass population is achieved, but gases are not managedand stripping of end products has not been practiced.

U.S. patent application Ser. No. 13/373,860 of Burke, entitled AmmoniaNitrogen Recovery Through a Biological Process, filed on Dec. 1, 2011,disclosed use of a biofilm in a rotating photobioreactor (RBC) tosupport bicarbonate consumption through the growth of autotrophicorganisms, thereby increasing the pH and shifting ammonium to ammoniagas for subsequent stripping. That application claimed a process wherebythe pH was increased and the ammonia gas stripped in the same reactorwithout the use of chemicals, as shown in FIG. 2. Ammonia gas wasproduced and stripped, thereby reducing end-product inhibition whilemaintaining concentrated biomass for maximum ammonium to ammoniaconversion. The configuration specified in U.S. patent application Ser.No. 13/373,860 has many other applications, some of which are thesubject of the present invention. Important benefits of the processinclude the support of a large retained biomass population as a fixedfilm, removal of inhibitory end products while they are produced, easeof harvesting the biomass, and low energy inputs.

SUMMARY OF INVENTION

The rotating photobioreactor (RPB) was developed to overcome thenutrient removal limitations associated with conventional autotrophicorganism growth in ponds or reactors. The rotating photobioreactor (RPB)is an improved method of producing biomass for energy production, aswell as removing and concentrating nutrients from waste streams and/oreutrophic waters. The bioreactor is capable of providing high surface tovolume ratios (S/V) for maximum light exposure, photo-autotrophicgrowth, gas transfer, and oxygen production. The RPB can be open orenclosed. It can be mounted in a vessel such as a tank or placed in awater body. “Vessel” is broadly defined to include, without limitation,a container, receptacle, repository such as a tank, water body, lake,river or stream, liquid conveyance or transport channel. The RPB enablesefficient harvesting of concentrated nutrient laden biomass. Thoseattributes make the RPB an attractive, simple, economical, and scalablemethod for removing soluble nutrients (NPK) from waste streams. Theprocess is a low head gas production and management apparatus thatproduces oxygen, while consuming CO₂. The RPB is a sustainable nutrientwaste treatment technology that incorporates a method to economicallyconcentrate and separate the nutrient laden biomass for use as afertilizer or renewable energy source.

The RPB was originally developed as a method to increase the pH ofanaerobic digestate without the use of chemicals for the stripping andrecovery of ammonia nitrogen (Burke, U.S. patent application Ser. No.13/373,860, entitled Ammonia Nitrogen Recovery Through a BiologicalProcess, filed Dec. 1, 2011). It was known that autotrophs consumebicarbonate and thereby increase the liquid pH when the amount of carbondioxide present is low enough to be growth limiting. However, the use ofalgae or cyanobacteria presented a number of problems. Ammonia is toxicto autotrophs and significantly reduces their specific growth rate.Consequently, it was necessary to develop a large biomass for sufficientgrowth to occur and thereby consume the bicarbonate to provide anincreased pH at low specific growth rates. The development of a largecyanobacterial mass required a large phototrophic surface to volumeratio (S/V). But developing a large surface to volume ratio was hinderedby the color and turbidity of the digestate as well as turbidityproduced through autotrophic growth. The color, turbidity, andautotrophic concentration reduced the photic zone in which autotrophgrowth occurs. All of those deficiencies can be overcome by usingattached autotrophic growth apparatus, i.e., the RPB. Growth occurs onplates or rotating solid or semisolid surfaces constructed of a varietyof materials upon which organisms attach and form a biofilm.

The process/apparatus, called an attached growth, rotatingphotobioreactor (RPB), uses natural or genetically-engineered organismsthat attach to a rotating support media upon which autotrophic organismsgrow. The media consists of a series of plates or plate-shaped mediathat maximize light exposure and gas exchange within an enclosed or openreactor. An example of the apparatus is as shown in FIG. 1. Theattributes of the process are as follows:

-   A) Surface to Volume Ratio (S/V). The apparatus provides a very    large surface to volume ratio for light exposure as well as gas    transfer. The rotating photobioreactor is truly three dimensional    since the biomass growth surface is proportional to twice (i.e.,    both sides) the square of the plate diameter. Providing a rough or    contoured surface can increase that surface area. Turbid liquids can    be processed since the liquid depth over the biomass growth surface    is very low, permitting adequate light penetration. The diameter and    distance between the plates controls the S/V ratio. In a square    algae pond the total surface to volume ratio is equal to 1/d, where    d=depth, whereas in the same area the RPB S/V is equal to    approximately twice that of a pond (2/d) if d is approximately equal    to the disc spacing and no surface area enhancements are included.    That distance between the plates can be low if artificial light    sources (e.g., light-emitting diodes) are placed between the plates.-   B) Light Exposure—Light penetration is hindered in conventional    photobioreactors since the photic zone, that is a function of    turbidity, is commonly less than 4 inches. In the RPB, exposure to    light is independent of liquid depth and turbidity. Light can be    supplied by natural or artificial means. Light exposure is    controlled by the surface area of the rotating growth plates, the    radiant flux of light provided, and the speed of rotation. The    rotation speed can be controlled to maximize light exposure,    organism shading, and gas transfer. The rotation speed and enclosed    reactor provide a means to control temperature and exposure to    predation, thereby minimizing any adverse environmental effects. The    artificial light source can be easily accessed for repair and    maintenance since it can be located in the wall of the    photobioreactor. Typically the lights are above or between the    plates and above the water surface for ease of maintenance.-   C) Water Losses—The loss of water vapor may also be minimized by    condensing water vapor from the gases exiting the enclosed rotating    photobioreactor.-   D) Solids Retention Time—Most importantly, the reactor maximizes the    solids retention time of the organisms that remove chemical    constituents from the liquid or generate gases. The reactor can    produce a non-turbid effluent since the growth occurs on the    rotating plates. No matter the application, the RPB will produce    energy-yielding biomass or gases from the supplied CO₂. The biomass    can be recovered at a rate to maximize yield.-   E) Biomass Harvesting. Harvesting algae or cyanobacteria is    typically an expensive unit process representing 20 to 30% of the    total cost of algae biomass production. Commonly used processes    include centrifugation, flotation, flocculation with a variety of    flocculants and sedimentation, membrane filtration, ultrasonic    separation, froth flotation, and electrolysis. A variety of    harvesting technologies have recently been developed. Relevant    recent U.S. patents include U.S. Pat. No. 8,470,161 (electrolysis is    used to separate lipids within the bioreactor); U.S. Pat. No.    8,399,239 (an attachment element such as iron oxide, steel, iron,    silica, etc. is introduced to attach to the algae and thereby    improve removal through settling or magnetic means); and U.S. Pat.    No. 8,281,515 (algae are grown in aggregated clumps or on synthetic    fabric that is removed and recovered from the growth medium).

In contrast, the RPB attached biomass can be easily harvested. Theconcentrated solids can be removed from the rotating plates through anyof a variety of means such as periodic scraping or partial scraping witha blade to discharge the aggregated solids to the liquid media forremoval through settling. Concentrated biomass is preferably removedfrom the rotating surface of the growth plates with a vacuum suctiondevice that periodically removes a portion of the biomass from differentsections of the rotating surface like a record player stylus.Concentrated biomass at 10% plus is accumulated in a vacuum receiver.That biomass can be delivered to an energy producing process to recoverthe energy value as an oil, sugar, or biomethane gas. The biomass mayalso be further dried to produce a fertilizer in a powder or pelletform.

-   F) Nutrient Harvesting. Autrotrophic organisms can harvest soluble    nutrients in direct proportion to their growth rate. The growth rate    is generally controlled by the limiting nutrient, light. The    nutrients can subsequently be economically harvested with the    biomass.-   G) Gas Processing. It is necessary to supply CO₂ for autotrophic    organism growth while removing the inhibiting 0₂. Other gaseous    products that can be produced by the process such as butanol or    selenium can also be efficiently removed and subsequently condensed    at low pressure as shown in FIG. 2. “Product” is broadly defined to    include without limitation a recovered commodity produced from a    substrate through a physical or biochemical process. The process    provides the ability to remove and recover gaseous products at    atmospheric pressure while providing essential gases such as carbon    dioxide for organism growth with minimal energy input. It is a    volatile gas transfer reactor.

“Volatile” is broadly defined to include, without limitation, anevaporative or vaporous substance such as water, alcohol, and gases suchas ammonia (NH₃) that are evaporated at normal temperatures. Unlikeconventional photobioreactors, the gas supply containing CO₂ isdelivered at low atmospheric pressure. In other processes, such asbutanol production, the toxic end product, butanol can be easily removedby blowing gas across the surface of the plates as shown in FIG. 2, asopposed to energy-consuming gas stripping through foam-producing bubbleaeration.

-   H) Product Gas Concentration. The volatile product gases that are    stripped include water vapor, which dilutes the final, condensed    product unless steps are taken to overcome the dilution. The RPB can    incorporate a membrane concentration device that passes permeate    water vapor and latent heat back to the reactor thus producing a    higher concentration retentate product as shown in FIG. 3. In most    cases the higher concentration product has significantly greater    commercial value. For example higher concentration ammonia solutions    have value for the pretreatment of lignocellulosic biomass for the    production of energy. In another application the RPB concentration    process can be adapted to produce diesel exhaust fluid having a    concentration of 20% ammonia thereby reducing the discharge of NOx    to the environment. Diesel exhaust fluids are typically composed of    a 33% solution of urea in distilled water, thereby producing a 20%    reactive ammonia solution.-   I) Energy Inputs—The RPB energy inputs for liquid and CO₂ gas supply    are extremely low because it is a free-flowing, low gas pressure,    low liquid head process. Oxygen is removed at atmospheric pressure.    Unlike conventional photobioreactors, the gas supply containing CO₂    is continuously delivered at low atmospheric pressure. Gas transfer,    CO₂ in/O₂ out, as well as product gas removal are rapid and    unrestricted for the same reasons. Heat can be provided as needed to    maintain optimum operating conditions.-   J) pH control—The process can also control the pH of the liquid    through cyanobacterial consumption of bicarbonate. An optimal pH of    8.3 can be maintained or the pH may be increased to control    predation by other organisms or for stripping gases by simply    adjusting CO₂ inputs in the form of a gas or as bicarbonate. The    unhindered light exposure and ability to control the pH will provide    a degree of disinfection and predation control.-   K) Process Integration—The process produces large quantities of    oxygen that can be used for a variety of purposes. The effluent    liquid is fully saturated and can be supersaturated with oxygen. The    growth of autotrophic organisms will convert soluble nutrients to    solid biomass for removal. The oxygen generated can be used for a    variety of purposes such as wastewater treatment or stabilization    and biogenic drying of processed biomass solids. Ideally an RPB    would be placed between primary treatment units and the aerated    waste activated sludge treatment units at a wastewater treatment    plant to remove and reclaim nutrients and oxygenate the influent to    the secondary aeration tanks. The process can also be integrated    with solids composting. Anaerobic digestate solids are commonly    stabilized by composting the residual solids. The compost/drying    process can be integrated with the RPB process that produces oxygen    for composting while the composting process produces the CO₂ for the    RPB process as shown in FIG. 4. Such an arrangement reduces the    discharge of gases, including odorous compounds to the environment.-   L) Ammonia Stripping—Initially the process was developed to raise    the pH of anaerobic digestate, pass the high pH liquid through a    stripping tower, and then strip and recover the ammonia. However,    during the initial operation it was discovered that ammonia gas was    evolved as the liquid passed through the RPB and the pH increased    from an initial value of 8.3 to 10. The rapid emission of ammonia    gas, as the pH increased, created biomass toxicity since it was the    unionized ammonia that inhibited the cyanobacteria. A fan was placed    in the photobioreactor to remove gaseous ammonia. It became apparent    that the RPB could be used for both raising the pH and stripping the    ammonia in a common unit, as shown in FIG. 2, at significantly less    cost and power consumption than a conventional stripping tower.-   M) Managing End Product Toxicity—Removal of end products that    inhibit production of desired products is the goal of most    fermentation processes. Typically the processes to improve recovery    performance and reduce costs include adsorption, pervaporation,    liquid-liquid extraction, gas stripping, and reverse osmosis.    Reverse osmosis has the disadvantage of membrane clogging or    fouling. In contrast, liquid-liquid extraction has high capacity and    selectivity, although it can be expensive to perform. Gas stripping    by bubbling fine or coarse bubbles through the fermentation broth is    a simple but efficient way to recover volatile products from    fermentation. Gas stripping enables the use of a concentrated    solution in the fermentor and a reduction in end product inhibition.    However, gas stripping requires compressor and turbine energy.    Foaming has been a problem requiring toxic foam suppression    chemicals. Liquid-liquid extraction is another efficient technique    to remove solvents from the fermentation broth. Liquid-liquid    extraction has critical problems such as the toxicity of the    extractant to the microbial cell and emulsion formation.    Pervaporation is a membrane-based process that allows selective    removal of volatile compounds from the fermentation broth. Further    distillation is required. The rotating bioreactor facilitates a    stripping process that operates at low pressures by blowing gas    across the attached biofilm growth surface, as shown in FIGS. 2, 3-A    and 3-B. Foam is not produced with such an arrangement. The    disclosed process of stripping in attached growth bioreactors can be    applied to heterotrophic (FIG. 3-B) as well as autotrophic (FIG.    3-A) reactors.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1-A presents a general plan of a covered or uncovered rotatingphotobioreactor; and

FIG. 1-B is an elevational view thereof.

FIG. 2 is an elevational view of volatile gas stripping and recoveryutilizing the rotating photobioreactor as a combined bioreactor andstripping unit.

FIG. 3-A presents volatile gas stripping and concentration utilizing therotating photobioreactor as a combined bioreactor, stripping,concentration and recovery unit.

FIG. 3-B presents volatile gas stripping and concentration utilizing therotating biological contactor as a combined bioreactor, stripping,concentration and recovery unit.

FIG. 4 presents the rotating photobioreactor integrated with acomposting/drying reactor process.

FIG. 5-A presents an example of the membrane water vapor separationsystem; and

FIG. 5-B presents a cross-sectional view thereof.

DETAILED DESCRIPTION OF INVENTION

The rotating photobioreactor (RPB) is a fixed film reactor upon whichautotrophic organisms are grown as a biofilm. A basic schematic of thereactor is shown in FIGS. 1-A and 1-B. It consists of a series of solidor semi-solid rotating plates or discs (5) that support the growth of abiofilm. The photobioreactor can be open or closed, covered (10) oruncovered. It can be mounted in a vessel such as a reactor tank (9),stream channel or water body, waste conveyance channel, etc. The reactorcan use natural or artificial light (6). Lighting can be above (6),between (11), or below the rotating discs. The discs are supported on ashaft (8) and driven by any of a variety of drives (7) that can impart arotating movement to the media.

The media upon which the autotrophic organisms are grown may consist ofa variety of substances such as wood, cloth, porous ceramics, glassfiber, carbon fiber, etc. Modifying the topography or roughness of thesurface can increase the plate area. The RPB may incorporate a varietyof biomass harvesting devices (20) such as doctor blades that removeexcess biomass growth and discharge the mass to the liquid stream fordownstream removal.

Vacuum suction devices may remove excess growth from any portion of therotating discs and discharge the concentrated solids to a vacuumreceiver.

Operation of the rotating photobioreactor requires an influent stream(1) containing essential nutrients, light (6), and a carbon source suchas air with carbon dioxide (3), carbon dioxide, or bicarbonate. Whilerecovering nutrients, the reactors produce an effluent gas (4)containing oxygen. The reactor may operate at thermophilic, mesophilic,or psychrophilic temperatures depending on the requirements for thegrowth of organisms retained on the rotating media.

Growth of the autotrophic organisms removes a portion of the solubleessential nutrients from the influent stream and carbon dioxide from thegas stream to produce particulate biomass that can be harvested (25),thereby removing the essential nutrients from the liquid stream andproducing an effluent (2) deficient in nutrients. The rotatingphotobioreactor may also be used to harvest a variety of gaseouschemicals, such as ammonia, directly or indirectly produced by theautotrophic organisms. The RPB is a unique reactor in that the organismsare exposed to a liquid stream for a portion of the time and a gaseousstream for the remainder of the time. The fraction of the time exposedto either the liquid or the gaseous medium is controlled by the disksubmergence or liquid level within the reactor. Products within theinfluent, or produced in the liquid medium, are carried to the gaseousportion of the reactor and thereby stripped with a circulating gasstream (3).

FIG. 2 presents an illustration of the stripping and recovery process.An influent stream (1) such as anaerobic digestate containing dissolvedbicarbonate and dissolved ammonium enters an enclosed (10) rotatingphotobioreactor (9) having any of a variety of light sources (6) at alower pH. As a liquid flows through the RPB the autotrophic organismsconsume the bicarbonate causing the pH to increase from the influentvalue to values necessary to causes the ammonium to shift to ammonia gasthat can be stripped by a gas flowing over the surface of the rotatingplates. Supplemental bicarbonate (HCO₃) or carbon dioxide may be addedto the influent streams to control growth.

The liquid influent may enter at any of a variety of ports along thelower portion of the reactor. The influent may also contain recirculatedeffluent to dilute the influent concentration and bicarbonate asrequired to maintain autotroph growth. The stripping gas (3), deficientin the product to be stripped, enters the upper portion, or gaseousportion, of the RPB at any of a variety of ports along the RPB necessaryto achieve optimum gas flow over each plate surface. The stripping gasmay exit (4) the RPB at any of a variety of outlet ports along the RPBnecessary to achieve optimum product stripping and gas conveyance overeach plate surface.

The stripping gas (4) containing the stripped product is conveyed to acondenser (15) cooled by a chiller (12) operating at a temperature lessthan the photobioreactor wherein the stripped water vapor and product(4) are condensed to form a condensate product (21) to be used for anybeneficial purpose. The condenser produces an influent gas (3) deficientin the product that is then conveyed by a blower through a heater, ifnecessary, to the RPB to provide further stripping. Depending on theapplication the blower may provide sufficient heat. Excess stripping gascan be discharged and make up gas provided by a pressure and vacuumrelief valve (P&VR) (17).

The process of stripping any gas from a liquid stream also removes watervapor that, when condensed, reduces the concentration of the product inthe liquid stream since both liquid water and product are produced inthe condenser. The concentration of the condensate is directlyproportional to the product/water ratio of the stripped gas. As a resultmost stripping processes produce dilute solutions that have reducedvalue. In addition to producing a dilute solution the water vaporremoves substantial quantities of heat from the reactor. This is aproblem inherent in most stripping reactors. Minimizing the gas flowrate, stripping temperature, and condensing at higher temperatures willminimize dilution of the condensate product. Further concentration canbe achieved through the use of a gas permeable membrane or membranes(16). The concentration process consists of utilizing a high water vaporpermeable membrane such as a silicon gas permeable membrane SSP-M823,available from Specialty Silicone Products, Inc., Ballston Spa, N.Y.,which has a high permeability rate for water vapor (3,500+) and lowerpermeability rates for ammonia (500), and stripping gases such asmethane (80), nitrogen (25), and oxygen (50). The membrane is placedbetween the stripped gas stream and a plenum. A differential pressure isapplied between the stripping gas stream consisting of the strippinggas, water vapor, and ammonia gas (retentate) and the lower pressureplenum gas stream (18)(permeate) composed of water vapor with lowerconcentrations of the stripping gas and ammonia. After passing throughthe membrane the stripping gas is depleted of water vapor while theplenum gas (18) is enriched. The plenum gas is then combined with theinfluent stripping gas from the condensate unit, thereby enriching thestripping gas with heat, water vapor, and minor concentrations of theproduct such as ammonia without significant loss of latent heat as shownin FIGS. 3-A and 3-B.

As shown in FIGS. 3-A and 3-B, one or more water vapor permeablemembranes are installed on the stripping gas stream leaving the reactor,but prior to the chiller/condenser (15). The water permeable membranesare placed under a vacuum by the recirculating blower (11) and controlvalve (14), or another pressurization device, to cause the return flowof water vapor permeate with its latent heat to the photobioreactor.

The above-described product concentration process can be applied to avariety of stripping processes using a variety of substrates.“Substrate” is broadly defined to include, without limitation, a liquidstream or waste substance containing Nitrogen, Phosphorus, Potassium andother essential nutrients, including light required for autotrophic orheterotrophic organism growth, including organic compounds derived fromthe pretreatment or hydrolysis of cellulosic or lignocellulosic biomassselected from the group consisting of waste materials corn cobs, cropresidues, corn husks, corn stover, grasses, wheat straw, barley straw,hay, rice straw, switchgrass, waste paper, sugar cane bagasse, sorghum,soy, components obtained from milling of grains, trees, branches, roots,leaves, wood chips, sawdust, shrubs and bushes, vegetables, fruits,flowers, animal manure, human waste, sugar, algae, cyanobacteria andmixtures thereof. A highly concentrated aqua ammonia stream hassignificantly greater value if used in ammonia-soaking pretreatment oflignocellulosic biomass for renewable energy production (12+%) as wellas in the production of diesel exhaust fluids (20+%). The membranesystem presented here can produce both products.

The product recovery process (FIG. 2) and the product concentrationprocess (FIG. 3-B) described above may also be applied to heterotrophicbioreactors such as the RBC to strip and recover “end products” such asbutanol and other alcohols from fermentation processes without producingfoam or utilizing excess energy. The RPB may also be integrated withcomposting or compost drying without producing odors inherent in thoseprocesses. Such a low pressure integration is shown in FIG. 4. Thephotobioreactor (9) is coupled with a solids compost or compost dryingreactor (22). The photobioreactor receives a liquid or solid streamcontaining sufficient nutrients for autotrophic growth and produces aliquid stream deficient in nutrients. The photobioreactor also producesa biomass stream that can be harvested (25) for production of an organicfertilizer, input to the compost dryer, or converted to energy throughany of a variety of thermochemical or biological processes such asanaerobic digestion. The photobioreactor also produces oxygen that canbe stripped and transported through a suction or discharge blower (11)with or without a gas heat exchanger (27) to the enclosed biogeniccompost dryer (22). Wet solids (20) are also input into the compostdryer with or without photobioreactor harvested biomass. The highlyoxygenated organic biomass reacts in the reactor (22) producing carbondioxide, heat, and water vapor. The reduced and biogenically driedorganic compost is discharged from the reactor (22). The carbon dioxideenriched circulating gas stream containing heat and water vapor exitsthe compost reactor. The carbon dioxide gas stream may be cooled (26)and the condensate (24) recovered, a portion of which may be used in thephotobioreactor. Cooling for condensate recovery (26) and heating (27)for the compost/dryer may be provided by a heat pump (23). The CO₂produced in the compost/dryer (22) is then used in the photobioreactorto produce biomass and oxygen in the photobioreactor in a closed loopsystem. The process provides a means of compost drying withoutdischarging odorous gases to the environment.

REFERENCES

-   Casey, T. J. (1997). Unit treatment processes in water and    wastewater engineering. Chichester; New York: Wiley.-   Corbitt, R. A. (1990). Standard handbook of environmental    engineering. New York: McGraw-Hill.-   Demirbas, A., & Demirbas, M. F. (2010). Algae energy: Algae as a new    source of biodiesel. Springer.,-   Design of Municipal Wastewater Treatment Plants. (1992). Design of    municipal wastewater treatment plants. Alexandria, Va.: Water    Environment Federation; New York, N.Y.: American Society of Civil    Engineers. Droste, R. L. (1997).-   Eddy, M. &., Tchobanoglous, G., Burton, F. L., & Stensel, H. D.    Theory and practice of water and wastewater treatment. New York: J.    Wiley. (2003).-   Ezeji, T. C., Karcher, P. M., Qureshi, N., & Blaschek, H. P. (2005).    Improving performance of a gas stripping-based recovery system to    remove butanol from Clostridium beijerinckii fermentation.    Bioprocess and Biosystems Engineering, 27(3), 207-14.    doi:10.1007/s00449-005-0403-7-   Fulks, G., Fisher, G. B., Rahmoeller, K., Wu, M.-C., D□Herde, E., &    Tan, J. (2009). A review of solid materials as alternative ammonia    sources for lean nox reduction with SCR. Diesel Exhaust Emission    Control, 2009-2001.-   Gouveia, L. (2011). Microalgae as a feedstock for biofuels.    Heidelberg; New York: Springer. doi:978-3-642-17996-9-   Grady, C. P. L., Daigger, G. T., & Lim, H. C. (1999). Biological    wastewater treatment. New York: Marcel Dekker.-   Huang, J. C., Suárez, M. C., Yang, S. I., Lin, Z., & Terry, N.    (2013). Development of a constructed wetland water treatment system    for selenium removal: Incorporation of an algal treatment component.    Environmental Science & Technology.-   Hunter-Cevera, J. (n.d.). Sustainable development of algae biofuels.    In Sustainable development of algal biofuel.Pdf.-   Jiang, A., Zhang, T., Frear, C., & Chen, S. (2011). Combined    nutrient recovery and biogas scrubbing system integrated in series    with animal manure anaerobic digester.-   Kaminsky, W., Tomczak, E., & Gorak, A. (2011). Biobutanol-Production    and purification methods. ECOLOGICAL CHEMISTRY AND ENGINEERING,    18(1), 31-37.-   Lee, J. W. (2013). Synthetic biology for photobiological production    of butanol and related higher alcohols from carbon dioxide and    water. In Advanced Biofuels and Bioproducts (pp. 447-521). New York,    N.Y.: Springer New York. doi:10.1007/978-1-4614-3348-4_(—)22-   Lee, S. Y., Park, J. H., Jang, S. H., Nielsen, L. K., Kim, J., &    Jung, K. S. (2008). Fermentative butanol production by clostridia.    Biotechnology and Bioengineering, 101(2), 209-28.    doi:10.1002/bit.22003-   Lin, S., & Lee, C. C. (2007). Water and Wastewater Calculations    Manual. New York: McGraw-Hill.-   Microalgae: Biotechnology and Microbiology. (1994). Microalgae:    Biotechnology and microbiology. Cambridge; New York: Cambridge    University Press.-   Millar, D. N., & Adam, D. D. (2013). Background information on the    MSU-EPRI N2O offsets protocol. Background information MSU-EPRI N2O    offset.Pdf [EPRI Report] (EPRI Report).-   Ni, B.-J., Ruscalleda, M. L., Pellicer-Nacher, C., & Smets, B. F.    (2011). Modeling nitrous oxide production during biological nitrogen    removal via nitrification and denitrification: Extensions to the    general ASM models. Environmental Science & Technology, 45(18),    7768-7776.-   Pinder, R. W., Adams, P. J., & Pandis, S. N. (2007). Ammonia    emission controls as a cost-effective strategy for reducing    atmospheric particulate matter in the eastern united states.    Environmental Science & Technology, 41(2), 380-386.    doi:10.1021/es060379a-   SAB, E. P. A. (n.d.). Reactive nitrogen in the united states: An    analysis of inputs, flows, consequences, and management options.-   Spencer III, H. W., Peters, H. J., & Hankins, W. (2007). Design    considerations for generating ammonia from urea for NOx control with    SCRS.-   Stephanie Kato, A. R. E. (2004). Report To The Legislature Gas-Fired    Power Plant NOx Emission Controls And Related Environmental Impacts.    Gas-Fired Power Plant NOx Emission Controls And Re.Pdf (CA Report To    The Legislature).-   Sutton, M. A. (2011). The European Nitrogen Assessment. Cambridge    University Press.-   Ward, B. B. (2013). Oceans. How nitrogen is lost. Science (New York,    N.Y.), 341(6144), 352-3. doi:10.1126/science.1240314-   Zheng, Y. N., Li, L. Z., Xian, M., Ma, Y. J., Yang, J. M., Xu, X., &    He, D. Z. (2009). Problems with the microbial production of butanol.    Journal of Industrial Microbiology & Biotechnology, 36(9), 1127-38.    doi:10.1007/s10295-009-0609-9.

I claim:
 1. A process for removing and harvesting nutrients from anutrient-laden, liquid influent stream using autotrophic or phototrophicmicroorganisms growing in a rotating photobioreactor, said bioreactorincluding a vessel, a shaft mounted for rotation within said vesselabout a shaft axis, a plurality of axially spaced-apart, growth platesattached to the shaft, each of the plates having surfaces to which afixed film of the microorganisms is attached, means for rotating theshaft and plates about the axis, illumination means for shining lightupon the microorganisms, and means for harvesting the microorganismsfrom the growth plates, comprising the simultaneous steps of: (a)shining light upon the microorganisms with the illumination means; (b)feeding the carbon source into the vessel; and (c) feeding the influentstream past the growth plates such that the growth plates are partiallysubmerged within the stream, whereby, as they grow, the microorganismsremove nutrients from the influent stream, capture the nutrients inbiomass, emit oxygen gas, and convert the influent stream to anutrient-deficient effluent stream; and further comprising (d) using theharvesting means to remove a portion of the microorganisms from thesurfaces of the growth plates without diluting them in the effluentstream.
 2. The process according to claim 1, wherein the vessel isuncovered.
 3. The process according to claim 2, wherein the vessel is anopen water body.
 4. The process according to claim 1, wherein the vesselis covered.
 5. The process of claim 4, wherein the vessel is a reactortank.
 6. The process of according to claim 1, wherein the vessel is acovered or uncovered waste conveyance channel.
 7. The process accordingto claim 1, wherein the liquid within the vessel is maintained at adepth such that, while rotating, the growth plates spend between 35% and65% of the time within said liquid and the remainder of the time out ofsaid liquid.
 8. The process of claim 1, wherein the surfaces of thegrowth plates include one or more of wood, cloth, porous ceramic, glassfiber or carbon fiber.
 9. The process of claim 1, wherein the harvestingmeans includes doctor blades disposed adjacent to the surfaces of thegrowth plates and engageable with said surfaces to shave portions of themicroorganisms from those surfaces during rotation of the plates. 10.The process of claim 1, wherein the harvesting means includes one ormore suction devices to suction microorganisms out of the vessel. 11.The process of claim 1, wherein the harvesting means is usedcontinuously to remove portions of the microorganisms from the surfacesof the growth plates.
 12. The process of claim 1, wherein the harvestingmeans is used intermittently to remove portions of the microorganismsfrom the surfaces of the growth plates.
 13. The process of claim 1,wherein the carbon source includes one or more of air, carbon dioxide orbicarbonate.
 14. The process of claim 1, wherein the liquid influentcomprises anaerobic digestate.
 15. The process of claim 14, furthercomprising passing a stripping gas past the growth plates to stripoxygen and/or to harvest any volatile products produced by themicroorganisms as stripped gas.
 16. The process of claim 15, whereinsaid anaerobic digestate contains dissolved bicarbonate and dissolvedammonium, whereby the microorganisms consume the bicarbonate, causingthe pH of the liquid within the vessel to increase and convertingammonium to ammonia gas, which ammonia gas, together with water vapor,is stripped by passage of said stripping gas flowing past the growthplates as stripped gas.
 17. The process of claim 16, further comprisingadding supplemental bicarbonate or carbon dioxide to the influentstream.
 18. The process of claim 16, wherein some of the effluent isrecirculated through the rotating photobioreactor by adding it to theliquid influent stream in order to dilute the influent stream nutrientconcentration, including the bicarbonate therein.
 19. The processaccording to claim 16, further comprising inserting the stripped gasinto a condenser cooled by a chiller and operating at a temperature lessthan the temperature of the liquid in the vessel, whereby the strippedgas and water vapor are condensed to form a condensate product and a gasthat is deficient in said product.
 20. The process of claim 19, furthercomprising recirculating the gas that is deficient in said product pastthe growth plates for further stripping.
 21. The process of claim 19,wherein if the temperature of the gas that is deficient in said productis less than the temperature of the liquid in the vessel, furthercomprising heating said gas up to said temperature and recirculatingsaid heated gas past the growth plates for further stripping.
 22. Theprocess of claim 19, further comprising discharging excess stripping gasand/or providing make up stripping gas through a pressure and vacuumrelief valve.
 23. The process according to claim 19, wherein thestripping gas includes one or more of air, methane, nitrogen, carbondioxide and/or oxygen, comprising further concentrating the product bythe steps of: (a) conveying the stripped gas to an upstream side of amembrane disposed within a plenum, said membrane having a highpermeability rate for water and a lower permeability rate for thestripping gas, and said stripping gas stream comprising stripping gas,water vapor, and a product volatile vapor; (b) applying a differentialpressure between the upstream side of the membrane and an oppositedownstream side of the membrane, whereby water vapor passes through themembrane to the downstream side of the membrane as water vapor permeatewithin plenum gas, and the gas on the upstream side of the membranebecomes depleted of water vapor as plenum retentate gas; and (c)combining the plenum gas formed in step (b) with the retentate gas thatis deficient in condensate product to form a combined stripping gas. 24.The process of claim 23, further comprising passing the combined plenumstripping gas past the growth plates.
 25. The process of claim 23,further comprising passing the combined plenum gas through a heater toraise the temperature thereof up to the temperature of the liquid in thevessel, and then passing the heated, combined plenum gas past the growthplates.
 26. The process of any of claims 23, wherein the differentialpressure across the membrane is maintained by a recirculating blower andcontrol valve to cause the return flow of water vapor permeate with itslatent heat to the rotating photo bioreactor.
 27. The process of any ofclaim 23, wherein the effluent stream comprises a highly concentratedaqua ammonia concentrated to 2 to 12 percent (w/w) or more, suitable foruse in the pretreatment of lignocellulosic biomass for renewable energyproduction.
 28. The process of any of claims 23, wherein the effluentstream comprises a highly concentrated aqua ammonia concentrated to 20percent (w/w) of more, suitable for use as diesel exhaust fluid (DEF).29. The process of claim 1, wherein the illumination means providesnatural and/or artificial light to the microorganisms and includes meansto control the intensity of the light.
 30. The process of claim 29,wherein the rotational speed of the growth plates and the intensity ofthe natural or artificial light are set such that the pH of the liquidin the vessel is maintained within the range of 6.5 to 11.0.
 31. Theprocess of claim 1, further comprising converting the microorganismsremoved from the rotating bioreactor to organic fertilizer or to energy.32. The process according to claim 15, further comprising (a) insertingthe oxygen stripped from the rotating photobioreactor into a composter;(b) inserting wet solids into the composter; (c) composting the wetsolids in a composter, thereby producing carbon dioxide, heat and watervapor in the composter; (d) discharging from the composter reduced andbiogenically-dried organic compost; and (e) conducting a carbondioxide-enriched gas stream containing heat and water vapor away fromthe composter.
 33. The process of claim 32, further comprising coolingthe carbon dioxide-enriched gas stream in step (e) to form a condensate,and passing the cooled carbon dioxide past the growth plates in thevessel.
 34. The process of claim 33, further comprising heating thestripped oxygen in step (a) of claim 32 before inserting the strippedoxygen into the composter.
 35. The process of claim 15, wherein themicroorganisms include designer photosynthetic organisms forphotobiological production of butanol and related higher alcohols,whereby the stripped gas includes butanol or other linear or branchedchain alcohols.
 36. The process of claim 35, wherein the designerphotosynthetic organisms are derived from marine algae and/orcyanobacteria that are viable in either seawater or groundwater.
 37. Theprocess according to claim 35, further comprising inserting the strippedgas into a condenser cooled by a chiller and operating at a temperatureless than the temperature of the liquid in the vessel, whereby thestripped gas and water vapor are condensed to form a condensate productand a gas that is deficient in said product.
 38. The process of claim37, further comprising recirculating the gas that is deficient in saidproduct past the growth plates for further stripping.
 39. The process ofclaim 38, wherein if the temperature of the gas that is deficient insaid product is less than the temperature of the liquid in the vessel,further comprising heating said gas up to said temperature andrecirculating said heated gas past the growth plates for furtherstripping.
 40. The process of claim 38, further comprising dischargingexcess stripping gas and/or providing make up stripping gas through apressure and vacuum relief valve.
 41. The process according to claim 38,wherein the stripping gas includes one or more of air, methane, nitrogenand/or oxygen, comprising further concentrating the product by the stepsof: (a) conveying the stripped gas to an upstream side of a membranedisposed within a plenum, said membrane having a high permeability ratefor water and a lower permeability rate for the stripping gas, and saidstripping gas stream comprising stripping gas, water vapor, and ammoniagas; (b) applying a differential pressure between the upstream side ofthe membrane and an opposite downstream side of the membrane, wherebywater vapor passes through the membrane to the downstream side of themembrane as water vapor permeate within plenum gas, and the gas on theupstream side of the membrane becomes depleted of water vapor as plenumretentate gas; and (c) combining the plenum gas formed in step (b) withthe retentate gas that is deficient in condensate product to form acombined stripping gas.
 42. The process of claim 9, wherein theharvesting means includes one or more suction devices to suctionmicroorganisms out of the vessel.